Electron discharge device



Sept. 24, 1935. H. A. WHEELER ELECTRON DISCHARGE DEVICE Filed Jan. 30,1935 TTo RNEY5 Patented Sept. 24, 1935 ELECTRON DISCHARGE DEVICE HaroldA. Wheeler, Great Neck, N. Y., assignor to Hazeltine Corporation, acorporation of Delaware Application January 30, 1933, -Serial No.654,327

Claims. (Cl. Z50- 27) UNITED STATES PATENT oFFicE This invention relatesto electron discharge Y devices, and more particularly to devices ofthis character having five or more electrodes.

It is an object of this invention to provide a device which isparticularly well-adapted to perform the function of modulation. Arelated object is to provide a modulator valvewhich can be readilycontrolled by means of a grid bias voltage.

In a preferred embodiment for carrying out the above objects, there isprovided a vacuum tube having six electrodes, namely, anelectronemitting cathode and a plate, or anode element, in the spacepath between which are located four other electrodes. These four latterelectrodes are in the form of screens and grids and are located atsuccessively increasing distances from the electron-emitting element,the rst of these screens and grids being designated as closest to thesaid emitting element.

The term grid or grid-like electrode", as used in the specification andclaims, denotes an electrode by which, or through which, electrons maypass. The term screen denotes a form of grid-like electrode by which, orthrough which, electrons may pass and which ordinarily is maintained ata substantial positive potential with respect to the actual cathode.

A feature which makes the device according to this inventionparticularly well suited as a modulator is the construction of the gridwhich is the third of these screens and grids in point of distance fromthe cathode; this grid is formed of a mesh having a variable spacing orpitch. It is preferable that the greater portion of this third grid beof relatively fine mesh, or pitch, although a substantial portion may beof much coarser' mesh.

The second of these interposed electrodes in point of distance from thecathode is a screen preferably constructed with a ne mesh or pitch.

The fourth of these interposed screens is incorporated for use as anordinary screen-grid; and it is found that the device is operative whenthis fourth screen is omitted.

In the drawing:

Figure l illustrates an electron discharge device in accordance withthis invention, a portion of the glass-enclosing vessel being cut awayto show more clearly the position of the electrodes within;

Fig. 2 is a vertical sectional view of the device showing in detail itsconstruction and the'positions of the elements;

Fig. 3 is a broken diagram showing in perspective the construction ofthe elements and also indicating the manner of connecting operatingvoltages which place the device in an operative condition; v

Fig. 4 is a plan View, in section, of the electrode 5 construction; and

Fig. 5 is an enlarged illustration, partially in section, of the cathodeelectrode and the means for heating the same.

Referring to Figure 1, the device comprises an l0 evacuated glass bulbI0, the stem end of which is fitted into a bakelite base II in which areembedded seven projecting terminal lugs, numbered I2 to I8,respectively, adapted to fit into a suitable socket. An eighth terminalI9 is situated l5 at the top of the bulb in the form of a metallic capcemented to the glass. The electrodes of the device are supported by anumber of Vertical supporting wires embedded in a glass stem 20 formedon a reentrant portion 2I at the stem end of the 20 bulb (see Fig. 2).For the purpose of maintaining the supporting wires rigidly in theirupright position, there are provided two flat guides 22 and 23 of aninsulating material, such as mica. through which the supporting wiresproject. The upper 25 guide 22 is constructed to snugly iit within thedome-like end of the glass bulb.

The following electrode construction is employed: A cathode I in theform of a sleeve of very small diameter is centrally located within thebulb. This sleeve is preferably constructed of nickel coated withstrontium and barium oxides for the purpose of causing it to copiouslyemitelectrons when heated. For the purpose of heating the cathodesleeve, there is located within the sleeve a heater filament 38 of newire, preferably of tungsten, coated with ceramic insulation andthreaded back and forth within the sleeve in the form of a W as shown inFig. 5. The ends of the heater filament are connected to the large- 4odiameter terminal lugs I2 and I3 at the base.

vgrid-electrode 2 and also of the remaining electrodes about to bedescribed. The major axis of each ellipse is only slightly greater thanthe minor axis. v

A second grid-like electrode 3, here called an inner screen, isconstructed in the form of an elliptical cylinder by winding a helix ofwire which surrounds the first grid.2, the second gridlike electrodebeing supported on the two supporting wires 26 and 21. This second helixis of fine mesh, that is, has a small pitch, which is preferably uniformthroughout.

A third grid electrode 4, here called an outer grid, surrounds theelectrode 3, and is likewise formed by a helix of wire in the shape ofan elliptical cylinder supported on supporting wires 28 and 29; but thepitch or mesh of this electrode is not uniform throughout its extent.Throughout the greater portion, the pitch is very fine, but in one ormore small ranges, thepitch is substantially increased. A constructionof this third grid which has been found very satisfactory is one inwhich fifty turns of .004-inch diameter wire are wound so that the majoraxis is 0.360 inch and the minor axis 0.316 inch, the component turns,numbered from one end to the other, having the pitch indicated in thefollowing table:

Turn Pitch 1-18 014 inch 10-20 018 2l O26 22-23 018 24 012 2526 0l8 27050 28-29 018 30 034 31-32 01B 33-50 014 Surrounding this third grid,and supported on supporting wires 30 and 3I, is a fourth grid-likeelectrode 5, here called an outer screen, also constructed of a helix inthe form of an elliptical cylinder. 'I'his fourth grid-like electrodepreferably has a relatively fine mesh which is uniform throughout.

Finally, a plate 6, in the form of an elliptical cylinder, is providedwhich surrounds the entire grid-electrode structure, this plate beingsupported on supporting wires 32 and 33. The plate is preferablyconstructed of carbonized nickel and its axial length is not as great asthat of the other electrodes.

From the foregoing description, it is observed that the first, second,third and fourth grid-like electrodes, designated 2, 3, 4 and 5,respectively, are located at succeedingly increasing distances, in theorder named, from the cathode in the 'space path between the actualcathode and the Constructional data for the electrodes other than thethird grid electrode, or outer grid 3, which have been found verysatisfactory, are as follows:

Inner grid 2 major axis, 0.121 inch; minor axis, 0.96 inch; wound with25turns of .004 inch diameter wire with a .033 inch uniform pitch.

Inner screen l-major axis, 0.236 inch; minor axis, 0.167 inch; woundwith 33 turns of .005 inch wire with a .025 inch uniform pitch.

Outer screen i-major axis, 0.490 inch; minor axis, 0.460 inch; woundwith 33 turns of .005 inch diameter wire, with a .025 inch uniformpitch.

The connection of operating voltages which place the device in a veryadvantageous operative condition, particularly for use as a modulator,is illustrated in Figure 3. There is connected across terminal lugs I2and I3 a battery 34 (or other source of filament heating current) whichserves to heat a W-type filament 33 within the cathode sleeve, the saidcathode itself being nominally grounded by the ground connection atterminal I4. Batteries 35, 36 and 3l, or other sources of direct voltageare connected between ground and the terminals I6, I'l and I8,respectively, for applying l0 positive voltages to the inner screen 3,the outer screen 5 and the plate 6, respectively. A negative biasbattery 39 is connected between ground and the cap I9 for placing anegative bias upon the non-uniform mesh, outer grid 4. l5

With the above-described system of operating voltages, the action of thedevice is as follows: The heated cathode I emits electrons which areattracted to the inner screen- 3 by virtue of the positive voltageapplied to the latter. The elecil trons upon reaching the screen 3 aretraveling at a high speed so that most of them pass on through thescreen and approach the outer grid 4, the negative potential of whichretards the electrons and causes most of them to be attracted back tothe positive screen 3. This retarding action causes a cloud ofslowly-moving electrons to accumulate between the electrodes 3 and 4.Hence, the position of this cloud may be termed n a virtual cathodebecause of the fact that the electrons can be easily drawn away from thecloud in the same manner that they were originally drawn away from thevicinity of the actual cathode I. Since the screen 5 and plate 6 are ata positive voltage, a stream of electrons is 3" drawn from the virtualcathode, through the meshes of the grid-like electrodes 4 and 5 to theplate. Electrodes 4, 5 and 6 function similarly to the respectivecontrol grid, screen and plate of screen-grid tetrode tubes. The outerscreen 3 40 will usually have applied to it a source of positive voltagesomewhat less than that of the plate in the preferred manner ofscreen-grid tubes.

The electron-discharge device in accordance with this invention has beenfound to be very 4" useful where it is desired to exert a control uponthe action of a vacuum tube without actually introducing into a circuitor space path of that tube external elements which would not verysuccessfully cooperate. For example, the repeating portion of the tubemay be considered to have input terminals which are the outer grid 4 andthe virtual cathode, and to have output terminals which are the plate 6and the virtual cathode. Since the potential of the virtual cathode isthe u" same as that of the actual cathode, it is found that inputsignals impressed between terminals I4 and I9 will be repeated at theoutput between terminals I 3 and I4.

The desired modification of the input signals can then be effected byapplying the modifying voltage to the inner grid 2, that is, betweenterminals I4 and I 5. This modifying voltage may often be a simplealternating voltage, which then causes the entire device to operate as amodulator.' The effect of the voltage on the grid 2 is to modify theelectron stream which flows to the virtual cathode and hence indirectlyto modify the space current between the virtual cathode 70 and theplate.

Since the electrodes 4,` B-and 3 exert very little effect on the spacecurrent to electrodes 2 and 3, the inner and outer control grids 2 and 4may be operated quite independently of each other. For u amasar plishedwithout .affecting the action ot any modilying voltage applied to innergrid 2.- Thisvaria- .tion of the negative bias of the outer grid l is avery convenient expedient inasmuch as it permits a very simple controlof the responsiveness of the device..

The non-uniform sise of the meshes of control grid I, commonly known asthe variable-mu or gradual-cutoff type of grid, permits a wide range ofbias voltage to be applied without causing signal distortion andwithoutinterfering with the normal action of electrodes 2 and 3.

'I'he outer screen l may be omitted.' -but its presence greatly improvesthe results, particularlyA in obtaining the greatest responsiveness.This screen, in general, performs the function of a similar screen inthe well-known screen-grid tetrode, and is therefore usually given apositive voltage somewhat less than that of the plate.

It is usually desirable to carbonize the inner wall of the glass bulb orvessel, as indicated in Figure 1 by the 'dotted portion of the glass;this, however, is a renement which may be omitted.

v I claim:

1. An electron discharge device adapted to function as a bias controlledsignal translating device comprising a closed evacuated vesselcontaining a centrally located cathode, at least three substantiallyconcentric cylindrical grid-like electrodes surrounding said cathode andbeing ofy succeedingly increasing diameters, and a cylindrical platesurrounding said electrodes, the third fromthe cathode of saidelectrodes having nonuniform grid spacings and having impressedthereupon a negative poipntial, and the second from the cathode of saidelectrodes having impressed thereupon a positive potential, wherebyelectrons drawn from said cathode form, in eiIect,

a virtual cathode between said second and third electrodes, thenon-uniform grid spacings of said third electrode serving to permit awide range of -bias voltage to be applied thereto without causing signaldistortion and without interfering with the normal action of theinnermost two grid-like e1ectrodes.

2. An electron discharge device adapted to function as a bias controlledsignal translating device comprising a closed evacuated vesselcontaining a centrally located cathode, four substantially concentriccylindrical grid-like electrodes surrounding said cathode and ofsucceedingly increasing diameters, and a cylindrical anode surroundingthe said electrodes, the thirdl from the cathode of said grid-likeelectrodes having a grid spacing which is non-uniform and havingimpressed thereupn a negative potential, and the second from the cathodeof said grid-like electrodes having impressed thereupon a positive'potentiaL whereby electrons drawn from said electrons are drawn to saidanode from said 5 virtual cathode. thenon-uniform grid spacings y ofsaidthird electrode serving to permit a wide range of bias voltage to beapplied thereto without causing signal distortion and withoutinterfering with the normal action o! the two grid- 10 like electrodesnearest the cathode.

3. An electron discharge device accordin to claim 2 in which the gridspacing of each of' said lectrodes, except said third electrode, isuni'- orm.-

4. Anfelectron discharge device adapted to function. as a biascontrolled signal translating device, comprising a closed vesselcontaining a cathode, at least three grid-like electrodes near saidcathode and located at succeedingly increas- 20 ing distances from saidcathode, and a plate substantially surrounding said cathode and saidelectrodes. the third from the cathode of said electrodes havingnon-uniform grid spacings and having impressed thereupon a negativepotential, .25

.and the second from the cathode of said elec- Aing to permit a widerange of bias voltage to be applied thereto without causing signaldistortion and without interfering with the normal action of theinnermost two grid-like electrodes. 5. An lelectron discharge deviceadapted to function as a bias controlled signal translating devicecomprising a closed evacuated vessel containing a cathode, fourgrid-'like electrodes near said cathode and located at succeedinglyincreas- 4o ing distances from said cathode, and an anode substantiallysurrounding said cathode and said electrodes, the third from the cathodeof said grid-like electrodes having a grid spacing which is non-uniformand having impressed thereupon a ,negative potential, and the secondfrom the cathode of said grid-like electrodes having impressed thereupona positive potential, whereby electrons drawn from said cathode form',in effect, a virtual cathode between said second and third electrodes,and a positive potential applied to the fourth from the cathode of saidgrid-like electrodes and to said anode, vwhereby electrons are drawn tosaid anode from said virtual cathode, the non-uniform grid spacings ofsaid third electrode servingI to permit a wide range of bias voltage tobe applied thereto without causing signal distortion and withoutinterfering with the normal action of the two grid-like electrodesnearest the cathode.

HAROLD A.

